Sprinkler Winterization: Blowouts, Timing and Backflow Care

We may earn commission from links on this page. Lead-form submissions are forwarded to local inspector partners. How we research and review.

An underground irrigation system spends half the year doing nothing, and along the Colorado Front Range that idle half is the dangerous part. Water left sitting in buried lines, valve manifolds and the above-ground backflow preventer can freeze, expand and crack components that are expensive and annoying to replace in spring. Sprinkler system winterization is the routine that prevents it: shut off the irrigation supply, get the water out of the system and protect the exposed parts. This guide explains why the job matters at altitude, when to schedule it, how compressed-air blowouts compare with manual and automatic drain systems, how to treat the backflow device, and what a typical service call costs. Prices are broad industry estimates rather than quotes, and local rates vary by company and the number of zones.

Part of our Plumbing & Water guide — start there for the full picture →

What Sprinkler System Winterization Involves

Winterizing an irrigation system means removing enough water from the pipes, valves, sprinkler heads and backflow assembly that freezing temperatures cannot damage them. In most Front Range homes the work follows the same basic sequence:

1. Turn the controller off or to “rain” mode so it does not try to run zones during the winter.
2. Close the irrigation shutoff valve, usually located in the basement, crawl space or a utility room where the irrigation line branches from the household supply.
3. Drain or open the backflow preventer so water does not stay trapped in its body and test cocks.
4. Remove water from the lines with compressed air, gravity drains or a combination, depending on how the system was built.
5. Leave the valves in a safe position for winter, which is often partially open on the backflow device’s test cocks and closed on the main ball valves, depending on the manufacturer’s directions.

That sounds simple, and on a small two-zone system it can be. On a larger yard with eight or ten zones, drip lines and a backflow preventer mounted on an exposed riser, the details matter more. Each step has a way to go wrong, which is why many homeowners hand the job to an irrigation company.

Why Front Range Systems Need to Be Winterized

Colorado’s climate is hard on irrigation equipment. Freeze-thaw cycles are frequent, and a warm October afternoon can be followed by a night well below freezing. Water expands as it freezes. Inside a rigid pipe or a brass valve body, that expansion has nowhere to go.

The components most at risk tend to be:

• The backflow preventer. Most systems along the Front Range use a pressure vacuum breaker (PVB) or a similar assembly mounted above ground next to the house. Because it sits in the open air, it is usually the first part to freeze. Cracked bodies, split bonnets and damaged internal check valves are common spring discoveries.
• Valve manifolds. Zone valves sit in shallow boxes. Trapped water can damage diaphragms, solenoids and fittings.
• Lateral lines and fittings. Polyethylene and PVC can split, and threaded fittings can crack, especially in shallow runs.
• Sprinkler heads and drip components. Rotor and spray bodies hold water, and small drip parts can be damaged when ice forms inside them.

Freeze damage is not guaranteed. Some systems survive a mild winter with water still in them, and soil depth, pipe slope and local microclimate all play a role. The point is that the repair bill when something does crack is usually much larger than the cost of draining the system in the first place. A cracked backflow preventer can also leave the household water line exposed to a leak if the irrigation shutoff valve is not fully closed.

The same cold snaps that threaten irrigation lines also threaten indoor plumbing. The frozen pipes guide covers the household side of the problem, including which pipes are most vulnerable and what to do if one freezes.

When to Winterize: Timing Before the First Hard Freeze

The goal is to finish before the first hard freeze, not after it. On the Front Range that often means late September through October, although timing varies with elevation. Homes in the foothills and higher-elevation communities may see hard freezes earlier than homes on the plains in Denver, Aurora or Colorado Springs, and an early-season cold front can arrive with little warning.

A few practical considerations:

• Book early. Irrigation companies get busy in October. Appointment slots can fill weeks ahead, and the first forecast of a hard freeze tends to produce a rush of calls.
• Balance watering needs. Lawns and trees still use water in early fall. Some homeowners hand-water trees with a hose during dry stretches after the system is off, which is also a reasonable way to support landscaping through a dry Colorado winter.
• Watch the overnight forecast. A single light frost is not the same as a sustained hard freeze, but the above-ground backflow preventer is vulnerable even to a short cold night. If a freeze is forecast before the blowout appointment, some homeowners shut the irrigation supply and insulate the backflow device as a temporary measure.

Sprinkler shutdown is only one item on a seasonal list. The broader guide to winterizing a house places it alongside furnace care, gutters, attic air sealing and outdoor faucets.

Winterization Methods Compared

How a system is winterized depends mostly on how it was designed and installed. There are three common approaches.

Compressed-Air Blowout

The blowout is the most common method along the Front Range. A technician connects an air compressor to the system, usually at a blowout port or the backflow preventer’s test cock, then runs each zone in turn while pushing air through the lines. Water is forced out through the sprinkler heads until the spray becomes a fine mist and then mostly air.

A blowout works on almost any system, which is why it is the default. It does carry risks if done poorly:

• Excess pressure can damage fittings, heads or the backflow device. Technicians typically regulate air pressure to a level suited to the pipe material and system design rather than running a compressor wide open.
• Air without water moving through a dry line creates friction and heat. Running air for too long on an already-dry zone can damage plastic components, so zones are usually cycled briefly and sometimes more than once.
• Air through the backflow preventer in the wrong direction or at the wrong valve position can damage internal parts. Many technicians connect downstream of the backflow device and keep its valves positioned according to the manufacturer’s instructions.

A large-volume compressor matters more than a high-pressure one. Small home compressors may move too little air to clear a zone effectively, which is one reason DIY blowouts sometimes leave water pooled in low spots.

Manual Drain Systems

Some systems are installed with manual drain valves at the low points of each line. Winterizing involves closing the irrigation supply and opening those valves so water drains by gravity. The method only works if the lines were sloped correctly during installation and the drain valves are accessible. In practice, many installers and homeowners still follow a gravity drain with a quick blowout, because sags in the pipe can hold water.

Automatic Drain Systems

Automatic drain valves open when pressure drops in the line, letting water escape after each watering cycle. They can reduce the need for a full blowout, but they do not drain the backflow preventer, the valve manifold or every low spot in the system. Automatic drains can also wear out or clog over time. Treat them as a helper rather than a guarantee.

Protecting the Backflow Preventer

The backflow preventer keeps irrigation water, which can pick up fertilizer, soil and other contaminants, from being drawn back into the household water supply. It is also the most freeze-sensitive part of most residential irrigation systems because it sits above ground.

Common winterization steps for a pressure vacuum breaker or similar assembly include:

• Closing the irrigation shutoff valve upstream of the device.
• Opening the test cocks and positioning the ball valves as the manufacturer directs, so trapped water can drain and expansion space exists.
• Removing any remaining water during the blowout without forcing air backward through the check valves.
• Adding an insulated cover or wrap. Insulated backflow covers and bags are inexpensive and help with early and late cold snaps, but they are not a substitute for draining the device.

Many Colorado water utilities require backflow assemblies on irrigation systems to be tested, often annually, by a certified tester. Requirements vary by provider, so check with yours. The backflow testing guide covers who needs testing, how it works and what it typically costs. If the device needs repair or replacement, spring startup is a natural time to schedule the test.

Finding the Irrigation Shutoff Valve

Every in-ground system should have a dedicated shutoff valve between the household water supply and the irrigation line. In many Front Range homes it is in the basement or crawl space near the main water entry, mounted on the foundation wall closest to the backflow preventer outside. In some newer subdivisions it may be in a meter pit, a dedicated valve box in the yard or a utility closet.

Look for a ball valve or gate valve on a pipe that heads toward the exterior wall near the outdoor backflow device. Many also have a small drain cap or bleeder screw on the downstream side, which is used to drain the short section of pipe between the valve and the wall. Leaving that section full can allow a freeze-related split inside the wall, which is one of the more damaging failure modes because the leak may not be noticed until the water is turned back on.

The same area often contains an outdoor spigot supply line. If a hose bib is leaking or has already cracked, the guide to outdoor spigot replacement explains frost-free options and when a plumber is needed. Knowing where both shutoffs live is useful in an emergency, which is why it is worth labeling the valves with a tag or marker.

DIY vs Professional Blowouts and Safety

A DIY blowout is possible, and many homeowners do it every year. It requires a compressor with adequate air volume, the correct fittings for the blowout port, an understanding of the system’s layout, and patience to cycle each zone. Renting a tow-behind compressor can cost close to what a professional service call costs, which is one reason many homeowners hire the job out.

Safety considerations with compressed air include:

• Eye and face protection. Air and debris can blow out of sprinkler heads, fittings and the backflow test cocks at speed. Safety glasses are the minimum, and standing away from open heads during the blowout is sensible.
• Pressure limits. Compressed air stores energy. A fitting that fails under air pressure can fail more violently than one that fails under water pressure. OSHA’s general-industry rule for compressed air used in cleaning, for example, limits that use to under 30 psi with chip guarding and protective equipment. That rule applies to workplaces and cleaning tasks rather than irrigation blowouts, but it illustrates how seriously workplace regulators treat compressed-air hazards.
• Never stand over a valve box or the backflow device while air is being applied, and never leave the compressor connected unattended.

For homeowners who are unsure about pressure settings or the backflow device’s valve positions, a professional blowout is generally the lower-risk choice. A mistake on the backflow preventer can cost more than several years of service calls.

Spring Startup Basics

Winterization has a mirror image in spring. Turning the water back on carelessly can cause a water hammer that damages fittings, so startup is usually done slowly.

1. Wait until the risk of hard freezes has passed. On the Front Range, many homeowners and irrigation companies schedule startups in late April or May, depending on elevation and the forecast.
2. Close any drain valves and test cocks that were left open for winter.
3. Open the irrigation shutoff valve slowly, a little at a time, to let the lines fill gradually.
4. Bring the backflow preventer into service following its manufacturer’s sequence.
5. Run each zone and walk the yard. Look for heads that do not pop up fully, sprays hitting pavement, pooling water and soggy spots that could indicate an underground leak.
6. Schedule the backflow test if the water provider requires it.

EPA’s WaterSense program describes a four-step “Sprinkler Spruce-Up” for this kind of check: inspect, connect, direct and select. Its guidance includes looking for heads that are tilted or do not pop up fully, checking connections inside valve boxes, redirecting heads that spray driveways or sidewalks, and considering a WaterSense labeled irrigation controller that adjusts watering to weather or soil moisture. WaterSense also recommends a certified irrigation professional if a homeowner is unsure about repairs.

Spring is also when drainage problems show up. Water from irrigation leaks or misdirected heads can pool against foundations; the yard drainage guide covers grading and downspout fixes that work alongside a healthy irrigation system.

How Much Does Sprinkler Winterization Cost?

Costs vary by company, region, the number of zones and whether the visit includes extra work. As broad estimates rather than quotes:

• Standard residential blowout: often somewhere around $60 to $150 for a typical home, with larger systems or extra zones costing more.
• Spring startup: commonly priced in a similar range, sometimes bundled with the fall blowout at a discount.
• Backflow test: often billed separately; prices vary by provider and city.
• Backflow preventer repair or replacement: repairs to a cracked bonnet or internal parts may run from roughly $100 to a few hundred dollars, while a full replacement with labor can be more, depending on the device and access.
• Line or head repairs: usually billed per head or per hour plus parts.

Ask for a written quote that lists what is included.

Irrigation Systems and Home Inspections

Buyers are often surprised to learn that a standard home inspection does not include the sprinkler system. The ASHI Standard of Practice lists landscape irrigation systems among the items an inspector is not required to inspect. Some inspectors may note a visible backflow device or an obvious leak, but a full evaluation of zones, heads and controllers usually requires a separate irrigation specialist.

For homes bought between October and April, the system may already be winterized, and operating it during a freeze is not practical. Buyers in that position can ask the seller for maintenance records, recent backflow test results and the name of the company that services the system. A contingency or escrow holdback for a spring startup check is sometimes negotiated. Our guide to hiring a home inspector explains what a general inspection covers and when add-on specialists make sense, and the plumbing and water inspection hub lists related water-system topics.

References

• Sprinkler Spruce-Up — U.S. EPA WaterSense
• WaterSense Outdoor Water Use — U.S. EPA WaterSense
• ASHI Standard of Practice for Home Inspections — American Society of Home Inspectors
• 1910.242 Hand and Portable Powered Tools and Equipment, General — Occupational Safety and Health Administration

Buying a Front Range home with an in-ground irrigation system, or wondering what else the cold could damage before closing? Reach out to us and we can help you line up an inspector and the right specialists for the systems a standard inspection leaves out.